Electric power generation and distribution systems for small and medium sized aircraft 10, as shown in FIG. 1, typically comprise a generator 14 which is located on and driven by each of the aircraft's engines 18, 20, large main power feeders 22 capable of conducting twice the rated current required by the system during normal operation which are routed from the output of each generator 14, through the fuselage 26, to a centralized power center 12 located in the nose of the aircraft, and several hundred individual load distribution feeders 28 which distribute the electric power from this centralized power center 12 in the nose to the individual pieces of utilization equipment located throughout the aircraft 10. Weight considerations require that the main feeders along the length of the fuselage 26 to the power center 12 utilize parallel aluminum feeders 22a, 22b (see FIG. 2) as opposed to the single larger gauge copper feeder set used elsewhere in the distribution system. For a two engine aircraft 10 the generation and distribution channels are essentially symmetrical, and the following discussion will therefore concern itself with one channel.
In the power center 12 the main power distribution is controlled by a generator line contactor 30, see FIG. 2, which connects the electric power from the generator 14 to the main load bus 34, and by a bus tie contactor 32 which connects the load bus 34 to a tie bus 40. This connection allows electric power to be supplied to a load bus 34 by the unassociated (other channel's) generator, or by external power through an external power contactor 42. Power distribution to the individual pieces of utilization equipment is controlled by individual circuit breakers 36 which are coupled to the main load buses 34. These individual circuit breakers 36 are located in the cockpit behind the pilot and co-pilot on a large circuit breaker panel 38.
Protection of the main power distribution is provided by current transformers which are positioned throughout the distribution system to create zones of protection. Current transformers located within the generator 14 (not shown) define the entrance to a zone of protection which extends from the generator 14, along the length of the main feeders 22 to the load bus 34, at which point: a line current transformer 44 defines an exit to the zone leading to the load bus 34. An additional line current transformer 48 defines another exit to the zone leading to the tie bus 40. If the current sensed entering the zone from the generator does not equal the current sensed exiting the zone to the load bus 34 and to the tie bus 40, a short circuit exists within the zone, and the associated generator 14 and load bus 34 are electrically removed from the system. A tie bus current transformer 46 provides protection for the tie bus 40 when the bus tie contactors 32 are closed coupling one generator to both load buses 34. These tie bus current transformers 46 also provide protection for the tie bus 40 when an external power source (not shown) is connected to the load buses 34 with the addition of an external power current transformer 50. Protection for open circuits along the length of the parallel feeders 22a, 22b is provided by parallel feeder current transformers 52a, 52b which sense the current flow in each phase of the feeders 22a, 22b. If the current flow in phase A, for example, of parallel feeder set 22a does not equal the current flow in phase A of parallel feeder set 22b, the associated generator 14 is electrically removed from the system and the bus tie contactor 32 is closed to allow power to be supplied to the load bus 34 via the tie bus 40.
One shortcoming associated with this prior art distribution system is that the size of the main feeders 22 (see FIG. 1) required to minimize voltage drop from the engine 18, 20 to the centralized power center 12 in the nose during rated current loading conditions increases the system weight. Additionally, since the power center 12 is located in the nose of the aircraft 10 and the utilization equipment is distributed throughout the aircraft 10, the size of the individual load distribution feeders 28 must be increased for the same reason. On an aircraft each additional pound translates directly into increased fuel bum, and thus higher operating costs for the airline.
Increased costs are also introduced into the prior art distribution system by the method of construction of the power center 12 and circuit breaker panel 38 (FIG. 2). The power center 12 is constructed from discrete components which are bolted to a framework assembly and wired together by hand. The construction of the circuit breaker panel 38 requires that each individual circuit breaker (as many as 350) be hand soldered to an individual load distribution feeder 28 which is connected to the load bus 34 located in the centralized power center 12, and to another individual load distribution feeder 28 which will be connected to its associated piece of utilization equipment. In addition to the increased system costs introduced by the manufacturing method of the prior art distribution system, additional costs, as well as weight, are incurred due to the number of current transformers which are required to protect the system from wiring failures. These additional components also serve to lower the overall system reliability.
The present invention is directed at overcoming one or more of the above mentioned shortcomings.